N10-009 Question 78
Single answerSMTPS: 587A company is migrating users from an older email configuration to a more secure submission method for sending outbound mail from laptops and mobile devices on many different networks. The mail administrator wants clients to submit email securely to the organization's mail server while still allowing authentication before messages are relayed. Which port should the administrator configure on the client devices for this purpose?
- A
TCP 25
- B
TCP 110
- C
TCP 465
- D
TCP 587
Show answer and explanation
Correct answer: D
Explanation
The best answer is TCP 587. In real-world deployments, port 587 is used for authenticated SMTP message submission by end-user mail clients, often with STARTTLS to encrypt the session after connection establishment. This differs from TCP 25, which is primarily intended for SMTP relay between mail servers and is frequently filtered by providers to limit abuse. Port 110 is POP3 and only for retrieving mail. Port 465 is seen in some environments for implicit TLS SMTP, but 587 is the standard submission port recognized in common email best practices and standards guidance. This distinction matters in troubleshooting and secure client configuration because administrators often need to separate message submission from server-to-server transport.
- A. Incorrect.
TCP 25 is the traditional SMTP port used primarily for server-to-server mail transfer, not the preferred client mail submission port. While some clients can send on 25, many ISPs and networks block or restrict it to reduce spam, and it is not the recommended choice for authenticated message submission from end-user devices.
- B. Incorrect.
TCP 110 is used for POP3 message retrieval, not for sending outbound mail. A candidate might choose this if confusing incoming and outgoing email services, but it does not provide SMTP submission functionality.
- C. Incorrect.
TCP 465 is commonly associated with implicit TLS SMTP submission in many environments, but for Network+ objectives and modern best practice, TCP 587 is the standard mail submission port for authenticated clients using SMTP with STARTTLS. Choosing 465 reflects a common confusion between secure SMTP variants.
- D. Correct.
TCP 587 is correct because it is the standard message submission port for email clients sending outbound mail using SMTP submission, typically with authentication and STARTTLS. This is the practical choice for laptops and mobile users who need to send securely from various networks.